In Japan, various plastics are used in massive amount, and development of the technique for reclaiming the used plastics is an important issue. For reclaiming main types of used plastic products, there are developed a recycling method of utilizing the used plastics as resin materials for the same products again or other plastic products, a method of thermally decomposing the used plastics at high temperature into chemical raw materials, such as synthesis gas and cracked petroleum, a recycling method of chemically decomposing the used plastics and returning them to monomers for conversion into other chemical substances for reuse, and a method of directly utilizing the used plastics as fuel for steam generation, power generation, a cement kiln, etc.
Among various plastics treatment and reclaiming of chlorine-based plastic products, particularly, have become big problems. In Japan, about 1.7 million tons of polyvinyl chloride resin is produced per year. The polyvinyl chloride resin is used in forms integrated with metallic materials in various construction components, coated wires, electric equipment, etc., because of having good characteristics in fire resistance, durability, resistance against oil and chemicals, electrical insulation, strength, flame retardation, weather resistance, coloring flexibility, material cost, bonding, welding, etc. In the 1990s, chlorine-based plastics, including the polyvinyl chloride resin, have been judged as major sources of dioxin and have caused social concerns. At present, dioxin is considered to be generated with imperfect combustion when not only the chlorine-based plastics, but also wastes containing chlorine and aromatic compounds are incinerated. As countermeasures, it is proposed, for example, to reduce a rate of imperfect combustion by improving the performance of an incinerator, to expand the recycling system so as not to incinerate refuses, which contain chlorine, through separation of the refuses, and to cut the amount of chlorine-based plastics used. However, because polyvinyl chloride-based resins are fairly different in chemical properties from general hydrocarbon-based resins, troubles are more apt to occur when polyvinyl chloride is mixed in the waste resin to be recycled.
When organic chlorine-based resins, such as vinyl chloride, are incinerated, hydrogen chloride is generated and it damages an apparatus. In a thermally decomposing apparatus, particularly, hydrogen chloride gas flows into near a condenser along with low-molecular decomposed gas and, therefore, a wide region is damaged by hydrochloric acid. This raises a problem that such a thermally decomposing apparatus cannot be used to thermally decompose the organic chlorine-based resins, including the polyvinyl chloride resin. For that reason, there are proposed several techniques for dichlorinating the polyvinyl chloride resin, and for processing the polyvinyl chloride resin without using any high-temperature process.
For example, a plastic dichlorinating method comprising the steps of melting and kneading waste plastics containing chlorine-based resins, e.g., polyvinyl chloride and polyvinylidene chloride, and exhausting hydrogen chloride, which is generated due to a photolysis action and an pyrolysis action by irradiating the waste plastics in a molten state with an ultraviolet ray from a mercury lamp, is proposed as a method for dichlorinating waste plastics, which can realize dichlorination at comparatively low temperature in a short time, which can selectively decompose couplings between carbons in molecules, thus reducing a concentration of residual chlorine, and which can increase a fuel yield (Patent Document 1).
Furthermore, an apparatus of treating organic chlorine-based resins is proposed (Patent Document 2). For separately recovering hydrochloric acid and oil components from the organic chlorine-based resins, the apparatus separately includes a dichlorinating apparatus for heating the organic chlorine-based resins to 300-350° C. and separating chlorine gas, and a gasification modifying apparatus for heating the residue to 400-450° C. in the presence of a catalyst and decomposing and recovering low-molecular oil components. The chlorine gas separated in the dichlorinating apparatus is cooled and recovered as hydrochloric acid by a hydrochloric-acid recovering apparatus. A part of the oil components is evaporated and resulting combustible gas is burnt in a gas combustion chamber such that combustion exhaust gas is reused as heat sources for various places. The proposed apparatus can realize a simplified and more compact structure, a cost reduction, and energy saving.
Moreover, it is proposed to dichlorinate plastic mixtures by heating them to 200-350° C. in a solvent capable of dissolving or swelling plastics, aliphatic hydrocarbons (heavy oil, light oil, and kerosene oil) or aromatic hydrocarbons (crude naphthalene oil, crude naphtha oil, creosote oil, anthracene oil, and tar) (Patent Document 3). In addition, it is reported, by way of example, that when recycling waste plastics including chlorine-based plastics, such as polyvinyl chloride, triethylene glycol is most effective in a dichlorination process using ethylene glycol, diethylene glycol, triethylene glycol, or propylene glycol as a solvent and KSCN as a nucleophile under the presence of alkali.
When treating products in which the organic chlorine-based resins are mixed or integrated with metallic materials, a more difficult step of separating the resins and the metallic materials from each other is required in addition to the dichlorination.
A technique for treating wastes and products including organic materials, e.g., plastics, and valuable metals, e.g., iron and non-iron metals, in mixed states basically comprises steps of treating the organic materials and recovering the valuable metals. As dry-process techniques having widely been used so far, there are techniques for treating the organic materials, such as a incineration method and a thermal decomposition method, and techniques for recovering the valuable metals, such as a magnetic separation method for recovering iron, an eddy-current separation method for recovering non-iron metals, and an air classification method for separating aluminum and copper. In practice, however, those known methods cannot separate metals and plastics from each other with high efficiency, and cannot selectively recover copper wires from coated copper wires and enameled wires. Although it is conceivable to add a step of air classification, gravity liquid separation, selection using a metal locator, stainless separation using a super-strength magnet, air-table gravity separation, etc., any step has not succeeded in solving the problem of recovering the copper wires. Recently, an amount of useless coated wires has increased year by year. For coated wires having large diameters and exhibiting high recycling efficiency, metals are reused by incinerating them at high temperature or by mechanically removing coatings therefrom. However, thin wires are presently disposed of as industrial wastes because an amount of recoverable metal copper is small and profits are not expectable with the above-mentioned methods.
As wet-process techniques, there are techniques for treating the organic materials, such as a wet oxidation method, a supercritical water-splitting method, and a supercritical hydroxylation method. In treatment of the organic materials, a decomposition process utilizing high-temperature hot water, e.g., supercritical hydroxylation, has a problem in application to the organic chlorine-based resins for the following reason. Because of decomposition in water, it is required to pulverize the organic materials, such as plastics, into particle diameters of about 0.1 mm, to previously separate and remove valuable metals, e.g., non-iron metals and copper wires, having particle diameters of not larger than 5 mm, which are difficult to be separated by ordinary separation equipment, with high efficiency from the viewpoint of preventing accumulation and clogging in a reaction vessel, and to previously remove plastics containing chlorine, such as polyvinyl chloride, with high efficiency. Thus, a practically useful technique capable of separating industrial wastes containing the organic chlorine-based resins and the metallic materials into metals and resins and effectively utilizing them is not yet developed.
Meanwhile, a massive amount of waste oil is generated and techniques for treating and reclaiming the waste oil are important issues in Japan. For example, lubricating oil is widely used in driving equipment, such as internal combustion engines, vehicles, machine tools, and industrial machines. In particular, consumption of engine oil, cylinder oil, hydraulic oil, extreme-pressure lubricating oil, cutting oil, etc. has sharply increased due to widespread use of automobiles caused by recent rapid motorization, mechanization of work to deal with labor shortage, etc. Those various types of lubricants become waste oil at a point in time when their properties have deteriorated after use for a so long time. The waste oil is treated, for example, by removing deteriorated components and mixed ingredients in the deteriorated oil (e.g., cutting oil, gear oil, and quenching oil) and reusing it as a lubricant, by processing the deteriorated oil to be usable as a substitute for heavy oil, by employing the deteriorated oil as supplemental fuel in a kiln, etc., and by incinerating it.
For example, when processing the waste lubricating oil to be usable as fuel, various additives are mixed into the lubricating oil, and heavy metals may be contained therein. If the waste lubricating oil containing the heavy metals is reused as boiler fuel, etc., the heavy metals are mixed into ash, thus causing environmental pollution. A technique for removing the heavy metals from the waste lubricating oil is proposed to cope with the above-mentioned problem (see, e.g., Patent Document 4).